1. Technical Field of the Invention
This invention relates to bearing protectors, specifically of the non-contacting labyrinth seal type and their use in rotating equipment, especially equipment which provides axial movement between the rotor and stator.
2. Description of the Prior Art
An example of a piece of rotating equipment which has axial movement between the rotating shaft and stationary housing, is a double ended centrifugal pump with bearing assemblies supporting the rotating shaft, at either end of said shaft. During operation, thermal growth of the shaft often occurs and the pump design typically accommodates this by providing an axially fixed shaft end and an axially floating shaft end.
In such equipment, each bearing arrangement typically consists of at least one bearing housed in a bearing chamber. Said bearing is lubricated and sealed between the rotor to stator interface to prevent the ingress or egress of a fluid or solid to the bearing cavity, since such unwanted material results in the deterioration of equipment life.
Bearing seals are often also referred to as bearing protectors or bearing isolators. However, the use of such seals extends well beyond the protection of a bearing in rotating equipment. Accordingly, while reference will be made below to bearing protectors, it should be understood that this term is used, as far as the invention is concerned, in connection with devices having wider uses.
The purpose of a bearing protector is to prevent the ingress of fluid, solids and/or debris from entering a bearing chamber. Equally, bearing protectors are employed to prevent the egress of fluid or solids from a bearing chamber. Essentially, their purpose is to prevent the premature failure of the bearing.
Non-contacting bearing protectors can be of repeller or labyrinth configuration. Reference is made to our co-pending labyrinth seal bearing protection application GB0415548.7 discloses a substantially non-contacting bearing protector with a static shut off device.
In a non-contacting bearing protector, the rotating component typically has a complex outer profile which is located adjacent and in close radial and axial proximity to a complex inner profile of the stationary component. Together these complex profiles, in theory, provide a tortuous path preventing the passage of the unwanted materials or fluids.
Conventional labyrinth seal technology indicates the close by adjacent axial counter rotational members are substantially parallel to each other and run perpendicular to the centreline of the shaft. Unfortunately, labyrinth seal technology has limited effectiveness at discouraging fluid, specifically in applications such as double-ended centrifugal pumps where axial displacement is expected between the shaft and the housing.
Axial movement of a rotor to a stator with a close axial relationship can lead to contact and frictional heat generation.
It is therefore deemed advantageous if a mechanism is created which accommodates axial shaft movement of rotating equipment comprising of a non-contacting bearing protector whilst permitting the effective sealing of the bearing lubricant fluid at all times.
Several attempts have been made to satisfy this basic sealing requirement, including Orlowski, U.S. Pat. No. 5,498,006 which teaches a plurality of radial pins projecting from the stator into a corresponding groove in the rotor. Orlowski relies on the clearances between the walls of the pins and the width of the rotor groove, to accommodate axial movement between rotor and stator.
The experienced reader should note several technical drawbacks with Orlowski U.S. Pat. No. 5,498,006, as follows;                the radial pins do not form a continuous annular surface, adjacent to the corresponding annular surface of the rotor groove. This leads to accelerated wear of the pins. The worn particles from the pins are dispersed adjacent and into the sealed bearing lubrication fluid. Said contaminates deteriorate the lubrication media leading to premature bearing failure;        as the bearing seal in Orlowski U.S. Pat. No. 5,498,006 is installed into the equipment housing, the seal stator is pushed into the equipment housing stator via a suitable hydraulic press or pressing action. Given this action, the axial forces are transmitted from the rotor to the stator through the brittle pins, which can create irreversible damage, including pin breakage;        the axial clearance between the pins and the rotor groove, must be replicated at each axial location between the rotor and stator, otherwise rotor to stator contact will result. As axial movement of a double ended centrifugal pump can be typically +/−2 mm (+/−0.080″). Such axial clearances at all locations between the rotor and stator, of U.S. Pat. No. 5,498,006, compromise the sealing integrity of the teaching;        both Orlowski U.S. Pat. No. 5,498,006 and our co-pending application GB0415548.7 describe the importance of a sealing device, which provides sealing between the rotor and stator when the equipment is not in operation. Clearly, despite a requirement for such a device in bearing seals, the teaching described in Orlowski U.S. Pat. No. 5,498,006 is unable to accommodate said beneficial feature due to the way in which the large amount of axial movement accommodated within the device; and,        typically, bearing seals incorporate a sealing elastomer between the seal stator and the equipment housing, however the sealable of the device in U.S. Pat. No. 5,498,006 has been compromised since said stator-housing seal has been omitted in preference of the plurality of radial pins. The reader will relate to the physical space constraints of the typical bearing seal installation and the limited alternate location of Orlowski plurality of radial pins, by design.        
It is thus deemed to be further advantageous if said axial accommodating mechanism, incorporates a stator to rotor sealing device, which prevents vapour and/or moisture entry into the bearing chamber when the equipment is idle and not in operation.
Furthermore, it is deemed to be advantageous to provide a continuous annular surface between the rotor and stator given that the rotor may contact the stator, during installation or operation.
Lastly, an invention which maintains traditional labyrinth axial clearances, which are typically 0.2 mm (0.010″) between the stator and rotor yet accommodates any amount of axial movement, including 4 mm (0.160″), is deemed advantageous given the dynamic sealing function is not compromised.